This invention relates to coating compositions for glass fibers and more particularly to an aqueous coating composition that includes the condensation product of a polycarboxylic acid or anhydride and a polyfunctional amine for coating glass fibers for use in reinforcing elastomeric products.
It has long been recognized that glass fibers should make an ideal reinforcement for automobile tires (U.S. Pat. No. 2,184,326), rubber timing belts (U.S. Pat. No. 2,135,057) and other rubber or rubberlike materials. In preparing glass fibers for such applications, glass fibers in the form of strands, yarn, roving or fabric are coated with an adhesive to aid in bonding of the glass to elastomeric material. By far the most widely used adhesive for preparing glass fibers for reinforcing rubber or rubberlike materials is a resorcinol-formaldehyde resin with an elastomeric latex. The resorcinol-formaldehyde resin is generally applied to glass fiber material prior to molding of the reinforced article by contacting a glass fabric, strand, yarn or the like with an aqueous latex mixture having the resorcinol-formaldehyde resin dispersed therein. Largely because of its high cost a satisfactory substitute for all or part of the resorcinol-formaldehyde resin has long been sought. Additionally the resorcinol-formaldehyde resin latex mixture is difficult to apply to glass fabric in a manner whereby the resin may thoroughly impregnate and coat the glass fibers which form the fabric. Therefore uncoated glass fiber strands often times remain in the fabric after being contacted with the resinous mixture. These strands are subject to glass on glass abrasion which soon destroys the long strands of glass and renders its reinforcing properties unsatisfactory. Further, resorcinol-formaldehyde resins in aqueous solution, over a long period of time, and when subjected to both ambient and superambient temperatures, have a tendency to further polymerize thereby changing the chemical and physical properties of the coatings formed therefrom.
It has been proposed that glass fiber materials be coated while being formed with a rubber adhesive in order to insure complete coating of a glass fiber with coating materials. For example, a glass fiber strand composed of a multitude of individual fine glass fibers or filaments formed by being drawn from a molten cone of glass located at the tips of small orifices in a bushing such as shown in U.S. Pat. No. 2,133,238 are contacted with a bath containing the adhesive material. However, difficulty has been encountered in coating glass fibers in this manner because the adhesive resorcinol-formaldehyde latex mixture remains tacky after application and drying and interferes with subsequent twisting, winding and spinning operations performed on the glass fibers to form roving, yarn, fabric and the like.
In a typical two-step operation glass fibers formed as described above are coated while moving at a high speed with the sizing composition containing a glass binder and lubricant to yield a strand comprising a multitude of individual glass filaments having sufficient integrity for workability in formation into yarn or the like. After the size has been applied to the glass, a number of strands in parallel form are coated with the coating composition, dried and then wound on a tubular support to form glass fiber roving which may then be formed by twisting, spinning or weaving into yarn fabric or other forms suitable for use as reinforcement for elastomeric products.
By sizing composition, as opposed to a coating composition, is meant a composition for coating glass fibers useful for reinforcing rubber and rubberlike materials characterized by a weight gain of glass fiber material when subject to a sizing treatment of about 0.5 to 2 percent based upon dry glass as opposed to a weight gain of about 15 to 40 percent based upon dry glass in a coating application wherein a rubber adhesive is applied to the glass fiber material.
A sizing composition or size is usually an aqueous dispersion including the addition of a lubricant, a coupling agent or finished material. The coupling agent or finished material renders the surface of the glass fibers compatible with the resin with which they are to be employed in preparing a glass fiber reinforced elastomeric product and aids in bonding the fibers thereto.
U.S. Pat. No. 3,718,448 entitled "Fiber Forming and Coating Process" by Warren W. Drummond and Donald W. Denniston assigned to the assignee of this invention discloses apparatus for applying a combined sizing and coating composition to individual glass fibers and then drying the fibers in strands and collecting the dried strands on a forming tube. By this process the glass fibers are simultaneously coated with both the sizing and coating in a single step that reduces substantially the time and equipment required to process the glass fibers for use as a reinforcement in elastomeric products. The combined sizing and coating composition previously employed with this process included only resorcinol-formaldehyde as the resin constituent. There is a need therefore for a coating composition and/or a combined sizing and coating composition that may be more economically prepared and applied to the glass fibers and has increased stability over the conventional resorcinol-formaldehyde based adhesive compositions.